Process of producing urea.



JOHN E. BUCHER, OF COVENTRY,

. COMPANY, OF PROVIDENCE, RHODE ISLAND, A COBPORATION OF RHODE ISLAITD.

rnocnssor rnonucme UREA.

No Drawing.

To all whom it may concern:

l 3e it known that I, JOHN BUcHnR, a citizen of the United States,residing at Coventry, in the county of Kent and State highly solublecyanate,

' ure, the factor which, byopposing the forcovery of urea.

Heretofore, urea has generally been made by heating solutions of alkalicyanateswith solutions of ammonium salts of oxygen containin mineralacids, such as the sulfate and nitrate. In many cases, the resultingsolutions were then evaporatedto dryness and the urea extracted withsolvents such as alcohol or methylated spirit.

. In one form of my rocess, a strong solu-v ut' not necessarily) suchthat'of potassium, may be treated with the requisite uantity of ammonia,and, carbon dioxid is tion of preferably t on passed into this alkalinesolution; suit:

able temperature and pressure conditions being of course observed duringthe several steps of the process.

A considerable part'of the potassium precipitates out in the form ofpotassium bicarbonate with the formation of ammonium cyanate:

The ammonium cyanate, especially upon heating, changes to urea accordingto the well known equation:

2 I moonsoomm The transformation of ammoniumv cyanate (equation 2)into-urea, which latter is only slightly dissociated, is fairly completeand becomes practically quantitative upon evaporat ng the water. Thischange reduces the concentration of ammonium cyanate or the'lonsresulting from its dissociation and consequently it overcomes, in alarge meas'-' Specification of Letters Patent. v

ammonia Patented Oct. 2, 1917..

Application filed July 3, 1914. Serial No. 848,799.

n s'r s PATENT .oFnro. y

nnonn rsLAnn, Assrenon 'ro m'rnoerm raonuc'rs mation of potassiumbicarbonate, makes equation 1 incomplete.

If desired the concentration of urea may be made still higher by theaddition of solid alkali. cyanate either before or after the removal ofthe original precipitate of potassium bicarbonate. The strengthening ofthe solution by the addition of solid alkali cyanates is especiallyadvantageouswhen sodium cyanate, which is much less soluble thanpotassium cyanate, is used.

On account of the great; difference in solubilities, a strongsolutionof" urea with comparatively small quantities of the alkali-[compound is obtained. The

easily be separated from the alkali compounds in pure condition bytakingadvantage of the diifering rates of change of solu; bility withthetemperature.

Distillation of water may becarriedon under diminished pressure, or, ina current of carbon dioxid so as '-,to prevent. the change of alkalibicarbonate \to neutral carbonate either by loss of CO due todissociation or by neutralization duev to theformationof by thehydrolysis of cyanate or urea. 1

When sodium cyanate is used, the change of this sparingly soluble acidsodium carammonia. For example:

' Pure urea can only crystalhze from 'such a solution so long as thelatter remains unsaturated with carbonate. If now ammonia be added, theacidcarbonate will be changed to the much more soluble normal carbonate,and further large, quantities vof pure urea may be obtained bycontinuing the crystallization of theurea until the normal carbonatebegins to separate out.- The solution be saturated with carbon may thenagain dioxid to remove, by further precipitation a considerable part ofthe remaining sodium as bicarbonate, and the just described processmaybe repeated until the solution becomes too'much charged with ammoniumcarbonates. It is then returned to the initial part oftheprocess'for thepreparation of mumvv POFQQ... 9i ure award ng W ca tionl.

urea can very.

bonate to the more soluble normal carbonate offers another method ofseparating pure' urea and it may even be changed intention- .ally by theaddition of free alkali such as Many forms of apparatus may be used but,since those forms at present employed commercially in the ammonia-sodaprocess are peculiarly well adapted for this, method of preparing urea,no special apparatus need be exemplified.

' The sodium cyanate and the ammonia may be obtained from any source,but both are,

preferably obtained from atmospheric nitrogen. I prefer to fix thenitrogen according to the equation:

with a heated mixture of sodium carbonate, finely divided iron andcarbon as described in mp application for United States Letters atent,Serial Number 799,798, filed Nov. 7, 1913, and entitledMethod of fixingnitrogen, and then to distil out of the cyanid under diminished pressureas described in my U. S. Patent No. 1,094,976, The molten cyaniddistillate is then treated with air at a low red heat according to theexothermic reaction:

(4) NaCN-I -air=NaOCN-{-nitrogen.

This procedure, since it uses the molten cyanid as obtained from thedistillation process,-has the great advantage of not requiring theheating up and the melting of the cyanid, of giving out heat which canbe utilized, and. of giving a practically unlimited supply ofsubstantially pureatmospheric nitrogen for the cyanid forming operation(equation 3).

' One-half of the product may then be used directly as sodium cyanatewhile the rest is very readily converted into ammonia and sodiumcarbonate by the action of hot water,

or steam, thus furnishing both the cyanate and ammonia, as well as apartof the carbon dioxid, which are required in equation 1:

The alkali compounds as well as the carbon dioxid thus act cyclically,and air, water and carbon comprise all the elements entering into urea.This procedure because of using organic acids has the further advantageof avoiding the use of mineral acids, such as sulfuric, for neutralizingthe ammonia when such salts as ammonium sulfate are used for thepreparation of urea.

The above mentioned decomposition of cyanate or urea into ammonia duringthe process causes no loss of urea as it may be compensated by usingsomewhat more than 50% of the nitrogen required in equation 1 in theform'of cyanate so that this excess of cyanate may produce some of therequisite ammonia directly in the liquid in which the urea is to beprepared.

- I am aware that various changes ma be made in my process and that thesteps 0 the method, as I have described them by way of exemplification,may-be varied or alterv nated widely, without departing from the spiritof my invention, and I, hence, desire to be limited only by the scope ofthe appended claims. I

For example, instead of using ammonia and carbon dioxid; acid ammoniumcarbonate may be employed, and since both potassium cyanate and urea arehighly soluble, the former may be practically treated with acidammoniumcarbo'nate to form potas-' sium bicarbonate. In the case ofalkaline earth cyanates such as those of barium or calcium, where therelative solubility of normal acid carbonates is just the reverse ofwhat it is in case of sodium, it is highly desirable to effect theformation of the practically .insoluble normal carbonates as pertheequation s1ty for separation by crystallization ma be avoided. Hereit is only necessary to filter out the precipitated carbonate and thenevaporate directly to dryness in order to get the urea.

It should be here observed, therefore, that more 'or less evanescentlyduring the 'course ofthe process, as by introducing carbon dioxid intothe urea yielding mass.

Finally in certain of the appended claims the expression compoundcontaining carvso as to precipitate the metal substantiallyquantitatively, in order that even the necesis broadly bon united tonitrogen by. a plurality of i 7 bonds has been used, for want of abetter,

to cover such cyanogen compound deriva-.

tives as the cyanates; there being some uncertainty as to just what isthe actual structure of, for example sodium cyanate.

Having thus descri ed my invention what I claim is: a V

p 1. The process of forming urea which comprises reacting upon an alkalimetal cyanate withan ammonium salt of carbonic acid in the presence ofwater, to form am-- monium cyanate and a bicarbonate of saidalkalimetal, converting said ammonium cyanate intourea, concentratipg thelatter by adding solid alkali cyanate, and separating the urea from theresidues of the reaction by varying the temperature, where- 13o being byto utilize the difi'cring rates of change of solubility of the urea andsaid residues.

2. The process of forming urea whic comprises reacting upon a compoundcontaining-carbon united to nitrogen by a plurality of bonds as one ofthe constituents thereof, with an ammonium acidsalt of carbonic acid, toform a substance capable of converted into urea.

3. The process of comprises reacting with material which includes anammonium hydrogen carbonic salt, upon a compound containing carbonunited to nitrogen by a plurality of bonds to combine the carbon andnitrogen with the ammonia and to form .a carbomc salt.

4. The process of forming urea which comprises reacting upon a metalliccyanate with an ammonium salt of 'carbonic acid in the presence ofwater, to form ammonium d an acid salt of'carbonic acid,

said ammonium cyanate into urea and separating --the latter from theresidues of the reaction, 1n part at least,

, comprises reactmg upon a metallic cyanate by converting said acidsalt. to normal carbonate. p

5. The process of forming urea which with ammonium salt of carbonic acidin the presence of water, to form ammonium cyanate and an acid salt ofcarbonic acid, con-- verting said ammonium cfyanate into urea andseparating the latter rom the residues forming urea which I ate byintroducing of the reaction, in part at least, by convertin said acidsalt to normal carbonate by the addition of free alkali. 4

6, The. process of formlng ur a which comprises reacting upon a metalliccyanate with ammonium salt of carbonic acid in the presence of water, toform ammonium cyanate and an acid salt of carbonic acid, convertingsaldammonium c .anate into urea and separating the latter rom the residuesof the reaction, in part at least, by convertin said acid salt tonormal'carbonate by the addition of ammonia.

7 The process of forming urea which i 1 comprises reactmg upon ametallic cyanate with an ammomum salt of carbonic acid in to r'ormammonium the presence of water,

of carbonic acid,

cyanate and an acid salt converting said ammonium cyanate into 7 ureaand separating the latter from the residues of the reaction, in partatleast, by converting said acid salt to normal carbonfree alkali, thencausto crystallize out, and introdioxid to remove a considerallgali asbicaring the urea ducing. carbon able part of the remaining bonate. 1 i

In testimony whereof I haxe aflixed my signature, in the presence of twowitnesses. I JOHN'E. BUGHER.

Witnesses:

NORMAN E. Horn, THOMAS H. Ro mn'rs.

